When 49ers running back Brandon Jacobs sheds that much weight, well, he remains a very large human being.

Asked about Jacobs' weight loss Friday - he's dipped from 275 to 260 since the spring - coach Jim Harbaugh sounded as if it was news to him.

"(He lost) 15 (pounds) from the offseason?" Harbaugh asked.

The good news for the 49ers is that Jacobs, who is expected to assume short-yardage duties, remains industrial-size. The potentially better news is that the NFL's biggest back believes he's moving better than he did last year when he had his second-lowest rushing average (3.8) since 2006.

Jacobs, 30, signed a one-year deal with the 49ers in April after spending the first seven seasons with the Giants.

"I feel faster, I feel stronger, I feel like I'm playing with better leverage," Jacobs said. "My pads are down more. I'm really looking forward to these preseason games we've got coming up."

The 49ers hope Jacobs, who stands 6-foot-4, can help improve their third-down offense. San Francisco ranked 31st in the NFL in third-down conversion percentage (29.4) in 2011 and converted just 17 of 35 third-down attempts when needing two yards or fewer. In such situations last year, Jacobs converted 5 of 7 attempts, according to Pro Football Focus. Jacobs converted 17 of 24 attempts in all short-yardage situations (two yards or fewer).

"I do know one part of my role will be downhill, in between the tackles, the man who wants it more," Jacobs said. "That's pretty much going to be my role no matter what the game plan is, going downhill, in between the tackles, who wants it more, me or them."

Given his size, Jacobs is ideally suited for the smash-mouth role. But he's been dogged by criticism throughout his career that he doesn't consistently run hard.

After Jacobs ran over defenders in an 18-carry, 72-yard, one-touchdown performance against the Patriots last year, Giants defensive Justin Tuck said, "When that guy is motivated to play, he's tough, man."

In June, running backs coach Tom Rathman made it clear the 49ers didn't bring Jacobs in to run outside.

"He has to understand who he is as a player," Rathman said. "We need him to pack it up inside and run over guys, be physical as a ball carrier. If we want somebody to run outside, we'll put somebody else in."

The early signs have been encouraging.

During offseason workouts, Jacobs raved about the 49ers' strength-and-conditioning program. Jacobs began doing squats to build strength in his legs for the first time in his career. He didn't do the exercises before, fearing he would hurt his knees.

Of course, as Jacobs increased his lower-body strength, he also dropped 15 pounds. He may not look much different, but the 49ers hope a stronger, leaner Jacobs is a difference-maker in short yardage.

"Brandon is a guy, and you think back on his career, when he gets his shoulders squared to the line of scrimmage and gets a forward lean, he is something," offensive coordinator Greg Roman said. "He's a unique running back. We've seen a good amount of that."